I have only fired on coal engines, but I did get some cab time in the Eureka, but did not fire. Eureka is a very small engine, and did not seem that difficult for the crew to fire, as it was only one split log, Armstrong in the box. As for the coal, The K's are the easiest to actually get the coal in and placed. There is about a 3 step lead up to the door, and plenty of room. The 315 has only 3 feet of clearance from the coal doors when closed, to the fire door. 315's grate is only 21 inches wide, but nearly 8 foot deep, with keyhole shaped sides. The economy door is only 18" wide. We use a small scoop that has been shortened on the blade end, and we have shortened handles also. The clearance from door to door is real pain on the climb to Cumbres out of Chama with a full load of coal. You have to use your hips and back more then your arms to get the coal to the front of the box. Once the coal doors are open and the pile is a couple of feet back it gets a whole lot easier, as you can take a step and get a good sling on the shovel. But we don't use as much tonnage to get to the top as a big K unit does.
My $.02